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<div class="titlepage"><div><div><h5 class="title">
<a name="beast.ref.boost__beast__websocket__stream.async_read"></a><a class="link" href="async_read.html" title="websocket::stream::async_read">websocket::stream::async_read</a>
</h5></div></div></div>
<p>
          <a class="indexterm" name="idp136842848"></a>
Read a message asynchronously.
        </p>
<h6>
<a name="beast.ref.boost__beast__websocket__stream.async_read.h0"></a>
          <span class="phrase"><a name="beast.ref.boost__beast__websocket__stream.async_read.synopsis"></a></span><a class="link" href="async_read.html#beast.ref.boost__beast__websocket__stream.async_read.synopsis">Synopsis</a>
        </h6>
<pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span>
    <span class="keyword">class</span> <a class="link" href="../../concepts/DynamicBuffer.html" title="DynamicBuffer"><span class="bold"><strong>DynamicBuffer</strong></span></a><span class="special">,</span>
    <span class="keyword">class</span> <a href="../../../../../../../doc/html/boost_asio/reference/ReadHandler.html" target="_top"><span class="bold"><strong>ReadHandler</strong></span></a><span class="special">&gt;</span>
<a href="../../../../../../../doc/html/boost_asio/reference/asynchronous_operations/automatic_deduction_of_initiating_function_return_type.html" target="_top"><span class="emphasis"><em>DEDUCED</em></span></a>
<span class="identifier">async_read</span><span class="special">(</span>
    <span class="identifier">DynamicBuffer</span><span class="special">&amp;</span> <span class="identifier">buffer</span><span class="special">,</span>
    <span class="identifier">ReadHandler</span><span class="special">&amp;&amp;</span> <span class="identifier">handler</span><span class="special">);</span>
</pre>
<h6>
<a name="beast.ref.boost__beast__websocket__stream.async_read.h1"></a>
          <span class="phrase"><a name="beast.ref.boost__beast__websocket__stream.async_read.description"></a></span><a class="link" href="async_read.html#beast.ref.boost__beast__websocket__stream.async_read.description">Description</a>
        </h6>
<p>
          This function is used to asynchronously read a complete message from the
          stream. The function call always returns immediately. The asynchronous
          operation will continue until one of the following is true:
        </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
              A complete message is received.
            </li>
<li class="listitem">
              A close frame is received. In this case the error indicated by the
              function will be <a class="link" href="../boost__beast__websocket__error.html" title="websocket::error"><code class="computeroutput"><span class="identifier">websocket</span><span class="special">::</span><span class="identifier">closed</span></code></a>.
            </li>
<li class="listitem">
              An error occurs on the stream.
            </li>
</ul></div>
<p>
          This operation is implemented in terms of one or more calls to the next
          layer's <code class="computeroutput"><span class="identifier">async_read_some</span></code>
          and <code class="computeroutput"><span class="identifier">async_write_some</span></code> functions,
          and is known as a <span class="emphasis"><em>composed operation</em></span>. The program
          must ensure that the stream performs no other reads until this operation
          completes.
        </p>
<p>
          Received message data, if any, is appended to the input area of the buffer.
          The functions <a class="link" href="got_binary.html" title="websocket::stream::got_binary"><code class="computeroutput"><span class="identifier">websocket</span><span class="special">::</span><span class="identifier">stream</span><span class="special">::</span><span class="identifier">got_binary</span></code></a> and <a class="link" href="got_text.html" title="websocket::stream::got_text"><code class="computeroutput"><span class="identifier">websocket</span><span class="special">::</span><span class="identifier">stream</span><span class="special">::</span><span class="identifier">got_text</span></code></a> may be used to query
          the stream and determine the type of the last received message.
        </p>
<p>
          While this operation is active, the implementation will read incoming control
          frames and handle them automatically as follows:
        </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
              The <a class="link" href="control_callback.html" title="websocket::stream::control_callback"><code class="computeroutput"><span class="identifier">websocket</span><span class="special">::</span><span class="identifier">stream</span><span class="special">::</span><span class="identifier">control_callback</span></code></a> will be invoked
              for each control frame.
            </li>
<li class="listitem">
              For each received ping frame, a pong frame will be automatically sent.
            </li>
<li class="listitem">
              If a close frame is received, the WebSocket close procedure is performed.
              In this case, when the function returns, the error <a class="link" href="../boost__beast__websocket__error.html" title="websocket::error"><code class="computeroutput"><span class="identifier">websocket</span><span class="special">::</span><span class="identifier">closed</span></code></a> will be indicated.
            </li>
</ul></div>
<p>
          Because of the need to handle control frames, asynchronous read operations
          can cause writes to take place. These writes are managed transparently;
          callers can still have one active asynchronous read and asynchronous write
          operation pending simultaneously (a user initiated call to <a class="link" href="async_close.html" title="websocket::stream::async_close"><code class="computeroutput"><span class="identifier">websocket</span><span class="special">::</span><span class="identifier">stream</span><span class="special">::</span><span class="identifier">async_close</span></code></a> counts as a write).
        </p>
<h6>
<a name="beast.ref.boost__beast__websocket__stream.async_read.h2"></a>
          <span class="phrase"><a name="beast.ref.boost__beast__websocket__stream.async_read.parameters"></a></span><a class="link" href="async_read.html#beast.ref.boost__beast__websocket__stream.async_read.parameters">Parameters</a>
        </h6>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                  <p>
                    Name
                  </p>
                </th>
<th>
                  <p>
                    Description
                  </p>
                </th>
</tr></thead>
<tbody>
<tr>
<td>
                  <p>
                    <code class="computeroutput"><span class="identifier">buffer</span></code>
                  </p>
                </td>
<td>
                  <p>
                    A dynamic buffer to hold the message data after any masking or
                    decompression has been applied. This object must remain valid
                    until the handler is called.
                  </p>
                </td>
</tr>
<tr>
<td>
                  <p>
                    <code class="computeroutput"><span class="identifier">handler</span></code>
                  </p>
                </td>
<td>
                  <p>
                    Invoked when the operation completes. The handler may be moved
                    or copied as needed. The equivalent function signature of the
                    handler must be:
                  </p>
<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="keyword">void</span> <span class="identifier">handler</span><span class="special">(</span>
    <span class="identifier">error_code</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">ec</span><span class="special">,</span>       <span class="comment">// Result of operation</span>
    <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">bytes_written</span>   <span class="comment">// Number of bytes appended to buffer</span>
<span class="special">);</span>
</pre>
                  <p>
                    Regardless of whether the asynchronous operation completes immediately
                    or not, the handler will not be invoked from within this function.
                    Invocation of the handler will be performed in a manner equivalent
                    to using <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_context</span><span class="special">::</span><span class="identifier">post</span></code>.
                  </p>
                </td>
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<td align="right"><div class="copyright-footer">Copyright &#169; 2016, 2017 Vinnie Falco<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
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